To improve the success rate of new drug developments, pharmaceutical companies have increasingly relied on the use of biomarkers. Biomarker is a term with many meanings, one of which may include one or more measurable quantities that can serve as indicators of biological processes, statuses, or outcomes of interest. For example, prostate-specific antigen is a commonly used diagnostic biomarker for prostate diseases. Ideal biomarkers may lead to better understanding of mechanism of drug treatments; better prediction and monitoring of therapeutic outcomes, and better management of risks associated with drug toxicities.
Ideal biomarkers should not only be sensitive and specific to biological conditions of interest, but ideal biomarkers should also be easy and convenient to detect and measure, preferably in body fluids, such as blood, urine, and cerebrospinal fluid. Although large-scale gene expression analysis by microarrays has helped to identify relevant biomarkers. Suitable biomarkers are often not genes, but proteins; protein fragments; metabolites; and others. One of the reasons this is the case is that tissue specific gene expression variation is not easily measurable in body fluids. Despite many technical challenges connected with protein identification and measurement, current efforts are focused on finding relevant protein biomarkers.